The objective of this study was to evaluate the effects of physical form of starter and inclusion of hay in diet of preweaning dairy calves on the intake, performance, digestibility, ruminal development, and the mRNA expression of genes involved in the ruminal metabolism. Holstein × Gyr crossbred male calves (n = 38) were enrolled on trial between 1 and 9 wk of age, and were assigned to 3 treatments: pellet + flocculated corn starter (n = 13), ground starter (n = 12), and ground starter + 5% chopped Tifton hay (n = 13). Pellet + flocculated corn starter had 96% pellets (4 mm in diameter and 18 mm in length) and 4% steam flaked corn. The same starter of the Pellet + flocculated corn treatment was used in the treatments Ground and Ground + 5% Hay, but ground to pass a 3.2 mm sieve. Tifton hay was added at 5% as fed of the amount of starter supplied to calves of the Ground + 5% Hay treatment, chopped into 67.1% of long particles (>19 mm), 13.3% of medium particles (between 8 and 20 mm) and 19.6% of small particles (<8 mm). All calves were fed 4L/d of whole milk up to 63 d of age and were weaned at 64 d of age. Water and starter were offered ad libitum. Samples of ruminal contents were obtained from all animals at 30, 45 and 60 d of age to evaluate the pH, ammonia nitrogen and volatile fatty acids (VFA). At 55 d of age, apparent digestibility assay was performed using 18 animals (n = 6 per treatment). At 65 d of age, the 18 animals were euthanized to evaluate the development of the digestive tract. Significance was declared at P ≤ 0.05 and tendency P > 0.05 and P < 0.10. The physical form of starter and the inclusion of hay did not influence intake, performance, feed efficiency, apparent nutrient digestibility, energy partitioning, nitrogen balance, ruminal pH, ammonia nitrogen concentration, VFA and the development of the digestive tract. The mRNA expression of monocarboxylate transporter 1 (SLC16A1) was higher in the dorsal sac than ventral sac. A tendency to increase the level of mRNA expression of SLC16A3 (MTC4) transporter and SLC9A2 (NHE-2) were observed on ground treatment. The authors thank FAPEMIG for financially supporting this research.